The present invention relates to a superconducting magnet and a magnetic resonance imaging apparatus using the superconducting magnet, and particularly to a super conducting magnet suitable for an open-type MRI apparatus not giving block-feeling to a person to be inspected and an MRI apparatus using the superconducting magnet.
An example of a conventional superconducting magnet used for an MRI apparatus is disclosed in Japanese Patent Application Laid-Open No.10-179546. The conventional superconducting magnet described in the patent gazette is constructed in such that a coil container containing the superconducting magnet immerged into cooling medium of liquid helium also serves as a helium tank for storing the liquid helium, and a refrigerator for cooling the liquid helium is directly placed in the coil container (the helium container).
Further, a method, in which a flexible portion such as a bellows is placed between a refrigerator and a cryostat portion placing the refrigerator as an accommodation against vibration of the refrigerator, is disclosed in Japanese Patent Application Laid-Open No.11-16719. Although this method can certainly insulate the vibration between the cryostat and the cold head of the refrigerator, in order to secure the vibration insulation while the cooling performance is being secured, various kinds of such devices as described the above-described patent are necessary and accordingly the cost is increased.
However, the conventional superconductor for the MRI apparatus has the following problems.
That is, since the refrigerator for cooling the liquid helium is directly placed in the coil container, the vibration of the refrigerator is directly transmitted to the coil container, and the superconducting coil contained in the inside is also vibrated by the vibration to vibrate the generated magnetic flux. Since the vibration of the generated magnetic flux gives a bad influence to the image, no clear image can be obtained.
On the other hand, conventionally, since the coolant tank and the coil container are formed integrally, the apparatus inherently becomes bulky. When the apparatus becomes bulky, a space to receive the person to be inspected (hereinafter occasionally referred to as subject) is limited to give block-feeling for the person to be inspected upon inspection.
The present invention is made in order to solve the above problems. An object of the present invention is to provide a superconducting magnet in which the vibration of the magnetic flux generated by the superconducting magnet is suppressed so as to not give bad influence to an image by reducing the vibration transmitted from the refrigerator to the coil container containing the superconducting coil, and to provide an MRI apparatus using the superconducting magnet.
Another object of the present invention to provide an MRI apparatus which can be formed in compact and provide greater space for receiving a subject so as not to give block-feeling to the subject.
In order to accomplish the above-mentioned objects, a superconducting magnet, according to the first aspect of the present invention, comprises superconducting coils; coil containers, each of said coil container containing said superconducting coil together with coolant; and a refrigerator for cooling said coolant, said coil containers being arranged separately from and opposite to each other, a magnetic field space being formed between both of said coil containers, wherein
a coolant tank for supplying the coolant to said coil containers is provided separately from said coil containers, and said refrigerator is placed in said coolant tank, a coolant circulation passage connects between said coolant tank and said coil containers, cylindrical spaces are defined in said coil container, and magnetic poles formed from ferromagnetic bodies are arranged within said cylindrical spaces.
A ferromagnetic member may be arranged on a surface in a reverse side of an opposite surface of each of said coil containers. A connecting passage may connect between said coil containers each other, and lead wires connecting said superconducting coils in said coil containers to each other pass through the inside of said connecting passage. A flexible portion may be provided in an intermediate portion of said coolant circulation passage.
According to the second aspect of the present invention, a superconducting magnet comprises superconducting coils; coil containers, each of said coil container containing said superconducting coil together with coolant; and a refrigerator for cooling said coolant, said coil containers being arranged separately from and opposite to each other, a magnetic field space being formed between both of said coil containers, wherein
a coolant tank for supplying the coolant to said coil containers is provided separately from said coil containers, and an amount of said coolant in said coil container is a necessary minimum amount for maintaining superconducting coil in superconducting state.
According to the third aspect of the present invention, a superconducting magnet comprises superconducting coils; coil containers, each of said coil container containing said superconducting coil together with coolant; and a refrigerator for cooling said coolant, said coil containers being arranged separately from and opposite to each other, a magnetic field space being formed between both of said coil containers, wherein
cylindrical spaces are defined in said coil container, and magnetic poles formed from ferromagnetic bodies are arranged within said cylindrical spaces, and an angle of visibility in vertical direction defined by said magnetic poles as viewing an opening portion of upper and lower coil containers from a center of said superconducting magnet, is greater than or equal to 30.
A connecting passage connects between said coil containers each other, and lead wires connecting said superconducting coils in said coil containers to each other may pass through the inside of said connecting passage.
According to the fourth aspect of the present invention, a superconducting magnet comprises superconducting coils; coil containers, each of said coil container containing said superconducting coil together with coolant; and a refrigerator for cooling said coolant, said coil containers being arranged separately from and opposite to each other, a magnetic field space being formed between both of said coil containers, wherein
a coolant tank for supplying the coolant to said coil containers is provided separately from said coil containers, said coil container and said coolant tank are connected to a coolant passage, a crossover from said superconducting coil is arranged within said coolant tank, and said crossover and a permanent current switch are connected within said coolant tank.
A bed capable of mounting a body to be inspected and moving between said coil containers of said superconducting magnets opposite to each other; and a control unit for analyzing a nuclear magnetic resonance signal from the body to be inspected.